Photovoltaic cells have a number of uses, in the solar energy industry, in the electronics industry and elsewhere. For example, photovoltaic cells can be used in solar energy panels for converting solar energy to electricity. For good energy conversion efficiency, photovoltaic cells are generally fabricated from high-purity polycrystalline silicon, also known as “polysilicon”.
Accordingly, as interest in solar energy increases, there is a growing demand for photovoltaic cells and for polysilicon from which to fabricate the photovoltaic cells. One useful commercial process for producing polysilicon employs trichlorosilane as a starting material.
U.S. Pat. No. 4,526,769 to Ingle et al. describes a process for producing trichlorosilane and equipment for practicing that process. As described, the process is a two-stage process which combines the reaction of silicon tetrachloride and hydrogen with silicon with the reaction of hydrogen chloride with silicon. A two stage reactor can be provided with a first stage heated to a temperature of about 500° C.-700° C. and a second stage maintained at a temperature of about 300° C.-350° C. Each of the first and second stages of the reactor is charged with silicon particles. According to the patent, a mixture comprising hydrogen and silicon tetrachloride is flowed through the silicon particles in the heated first stage to cause a partial hydrogenation of the silicon tetrachloride. The effluent from the first stage is described as including trichlorosilane and unreacted hydrogen and silicon tetrachloride. Hydrogen chloride is added to this effluent and the mixture of gases is passed through the silicon particles in the second stage of the reactor.
Pursuant to the growing demand for solar energy grade photovoltaic cells and high-purity polysilicon, there is a need for improved processes and systems for producing trichlorosilane suitable for use in the manufacture of polysilicon.
The foregoing description of background art may include insights, discoveries, understandings or disclosures, or associations together of disclosures, that were not known to the relevant art prior to the present invention but which were provided by the invention. Some such contributions of the invention may have been specifically pointed out herein, whereas other such contributions of the invention will be apparent from their context. Merely because a document may have been cited here, no admission is made that the field of the document, which may be quite different from that of the invention, is analogous to the field or fields of the present invention.